We will examine the neural control of cardio-respiratory function using long-term recording of single neurons in defined areas of the brain stem and the forebrain during spontaneous sleep-wake cycling. The cardio-respiratory mechanisms that will be examined include cardiac and respiratory rate and their variability, apnea, spontaneous cardiac arrhythmia, sinus arrhythmia, blood pressure, skeletal and renal blood flow, and core and peripheral temperature. Interactions between neurons involved in cardio-respiratory control within the forebrain and brain stem will be examined using point process display and correlation techniques. These procedures will also be used to study relatibns between neuronal discharge and cardio-respiratory activity. Time series analyses techniques of spectra and coherence will be used to examine frequency-dependent interactions between neuronal activity and variability in autonomic function. In addition, variations in cardio-respiratory activity will be induced by 1) stimulation of forebrain regions, 2) CO2 challenges, and 3) total airway obstruction, Interneuronal as well as neuronal-autonomic interactions elicited by these experimental procedures will then be examined.